| 摘要 |
A four-wire communication system for interconnecting wideband lines is disclosed. The continuity and transmission characteristics of the selected network channels and the four-wire lines are tested prior to each use. The test is made by transmitting a predetermined signal over a pair of wires and, through a loopback arrangement, returned over the other pair of wires. The returned signal is then compared with signals of preselected value and if the test is satisfactory, the loopback arrangement is removed.
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